As described, for example, in Japan Patent Publication No. 36,360/76, (corresponding to U.S. Pat. No. 3,827,937) Japan Patent Publication No. 27,561/80 (U.S. Pat. No. 4,202,940 and U.S. Pat. No. 4,202,966) or Japan Patent Kokai No. 121,997/78, the glucan can be produced by culturing a strain of species Aureobasidium pullulans or genus Elsinoe on a nutrient medium containing sugars, such as corn syrup or sucrose, under aeration-agitation conditions, removing the cell debris, and recovering and purifying the resultant supernatant or filtrate.
In the production of self-supporting film with the glucan, the use of a high-purity glucan wherein impurities, such as inorganic substance, have been removed as much as possible, is recommended in order to increase its physical strength including tensile or folding strength. Thus, a high-purity glucan having a water-soluble inorganic substance content below 0.01% has been used in conventional self-supporting glucan film.
Film production using an aqueous solution of such high-purity glucan requires a careful selection of casting base so that the glucan solution can be cast thereon to give a uniform layer, and so that the resultant glucan film can be easily released therefrom: For example, an embodiment as disclosed in Japan Patent Publication No. 27,099/80, Japan Patent Kokai No. 13,565/79 (see CA91-20982 or Japan Patent Kokai No. 52,793/79 (U.S. Pat. No. 4,306,059) teaches the use of a metal plate or a chromium-plated metal roll. As apparent from the description of Japan Patent Kokai No. 13,565/79 or 52,793/79, a process comprising casting an aqueous glucan solution on such casting base, however, requires a large amount of fatty acid ester of sucrose as a mold release agent, as well as severe moisture-control during the subsequent step of releasing the resultant glucan film.
Despite of such requirements, a continuous production of self-supporting glucan film using an aqueous glucan solution has been deemed to be very difficult.
Accordingly, there has existed a strong need for a continuous process for producing self-supporting glucan film. As will become apparent from the following, the present invention does meet the need.